Any electronic devices loaded in automobiles, located outdoors, or used in a dusty environment need to be equipped with sealing components, such as gasket or grommet, which prevent ingress of water or dust from outside. These sealing components are provided to seal, for example, a gap between a cover portion and a body of a casing, a gap between a casing and a wiring unit such as a power supply line, or a gap between a plurality of casings joined with each other. Further, there is a prospect that an FPC (flexible printed circuit board) will be more often used in the wiring unit as automobiles and electronic devices are more space-saving and reduced in weight. In order to seal any section where the FPC is used, the sealing component is formed integral with the FPC to ensure a sealing performance in the wiring unit.
In the meantime, the EMC (electromagnetic compatibility) regulations for electronic devices are becoming more demanding in different industrial fields in recent years, which requires some overall measure for EMC compliance in circuit, casing and system. An effective EMC-compliant measure in casing is an electromagnetic wave shield which blocks radiation and penetration of electromagnetic waves. When any sealing component which is not electrically conductive is used, however, an electrical gap is generated where the sealing component is attached, and there is no way to avoid electromagnetic waves that may radiate and penetrate through the gap.
According to the invention disclosed in the Patent Document 1, a gasket which seals joined surfaces of a casing cover and a casing body is electrically conducted to provide an electric connection between the casing cover and the casing body so that an electromagnetic wave shield is formed across the casing. This technique, however, fails to form an expected electric connection between the casing and the electromagnetic wave shield layer of FPC because the surface of the electromagnetic wave shield layer of FPC drawn out of the casing is covered with a protective film formed to provide surface protection and electrical insulation. As a result, it may fail to substantially shield the electromagnetic waves because the shield layer possibly serves as an antenna, causing incident radiation of electromagnetic waves.